1. Field of the Invention
The present invention relates to a novel process for producing 2-vinylcyclododecanone.
2. Description of the Related Art
2-Vinylcyclododecanone is a synthetic intermediate of 5-cyclohexadecen-1-one classified into a category of the musk perfumery in the perfumery field. Known methods of synthesizing this 2-vinylcyclododecanone include a method in which vinylmagnesium chloride is made to act on 2-chlorocyclododecan-1-one to obtain 2-chloro-1-vinylcyclododecan-1-ol, which is then heated in the presence of magnesium ethylbromide (publication of JP-A-49-49936), a method in which 2-vinylcyclododecene oxide is made to react in the presence of a Lewis acid catalyst (publication of JP-B-53-31147) and a method in which vinylmagnesium chloride is reacted with cyclododecene epoxide to prepare 2-vinylcyclododecan-1-ol, which is then oxidized (publication of JP-B-55-34780).
However, the method described in the publication of JP-A-49-49936 gives rise to a safety problem because this method uses, as a solvent, benzene, whose carcinogenicity has pointed out, in the final step as shown in the following reaction formula. Also, because a chloro-compound is used as a reaction raw material, there is a fear as to the safety of chlorides remaining when 5-cyclohexadecen-1-one is finally produced. 
The method described in the publication of JP-B-53-31147, in turn, has the drawbacks that this method involves a water-washing step, solvent-recovery step and refining step, requiring complicated operations.
Also, the method described in the publication of JP-B-55-34780 is based on the reaction formula shown below. This method however has a low yield and benzene is used as a solvent, giving rise to a production problem. 
It is an object of the present invention to provide a process for producing 2-vinylcyclododecanone simply, efficiently and safely without involving any washing step, solvent recovery step and the like.
The inventors of the present invention have conducted earnest studies concerning a method of preparing 2-vinylcyclododecanone with high efficiency and, as a result, found that an equilibrium relation in terms of thermal isomerization is established between 2-ethylidenecyclododecanone and 2-vinylcyclododecanone, the isomerization equilibrium state can be reached in a short time by heating 2-ethylidenecyclododecanone in the presence of a specific isomerization catalyst, and 2-vinylcyclododecanone can be obtained with high efficiency if reaction distillation is further utilized. The present invention was thus completed.
Accordingly, the present invention provides a process for producing 2-vinylcyclododecanone, the process comprising isomerizing 2-ethylidenecyclododecanone represented by the following formula (1): 
wherein the wavy line shows that the double bond is a Z-isomer, an E-isomer or a mixture of an E-isomer and a Z-isomer; in the presence of a catalyst and separating 2-vinylcyclododecanone represented by the following formula (2) from the reaction product by fractionation: 